This invention relates in general to silver-oxide alkaline batteries and, in particular, to a process for making silver-oxide electrodes having a high efficiency in silver utilization.
As is well known divalent silver oxide (AgO) has a significantly higher capacity per unit weight than does monovalent silver oxide (Ag.sub.2 O). Thus when manufacturing high capacity batteries, especially where the weight and volume of the battery is critical as in aerospace applications, the higher capacity of divalent silver-oxide electrodes is advantageous. However, divalent silver-oxide electrodes formed by conventional anodizing of sintered silver produce a well-known voltage stabilization dip below nominal closed circuit potential when the battery load is first connected. Monovalent silver-oxide electrodes do not produce the voltage stabilization dip. Although divalent silver-oxide electrodes have a higher capacity than electrodes composed of monovalent silver oxide, the former lose capacity with age at a much greater rate. Thus where shelf life of the battery is critical, the aging characteristics of monovalent silver oxide offer advantages.
In certain aerospace applications, the silver-oxide alkaline battery for the electronics systems is not activated until immediately prior to applying the load to the battery. A voltage stabilization dip is unacceptable to the electronics and shelf-life is critical since the batteries must have a specified capacity even though the electrodes were formed long before battery activation.
In the past when making electrodes for this application, porous silver electrodes have been electroformed to the oxygen-evolution level where they exhibit the characteristics of divalent-silver oxide. In order to avoid undesirable characteristics of divalent silver oxide, the electrodes are further processed by electrochemical reduction techniques or chemical reduction techniques to convert some of the divalent silver oxide to monovalent silver oxide. In the electrochemical reduction techniques, the divalent silver-oxide electrodes are removed from the anodizing apparatus, washed, placed in a fresh electrolyte solution and backdischarged for four to six hours. In the chemical reducing technique, the anodized electrodes are placed in a hydrazine solution. Both prior art processes require substantial labor and, more importantly, result in a loss in capacity of as much as forty percent.